1. Field of the Invention
The present invention relates to a communication control device for passenger protection device, which is used as a supplemental restraint system (SRS) for protecting passengers when a vehicle collides.
Priority is claimed on Japanese Patent Application No. 2004-266644, filed Sep. 14, 2004, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, for example, a communication control device for passenger protection device includes, in a center unit, for example, a main controller provided near a center console, a floor sensor provided in a center of the vehicle, and a plurality of satellite sensors provided at the front and sides of the vehicle. The main controller determines a collision state of the vehicle based on signals which are output from the floor sensor and the satellite sensors, and controls the activation of airbags.
The floor sensor is generally installed near the main controller and connected directly to it, or contained inside the main controller. In contrast, the satellite sensors are installed on a front band and near B pillars of the left and right doors. Output signals from these satellite sensors are transmitted via communication cables to the main controller. For example, the satellite sensors digitize detection signals and send them constantly to the main controller. Each satellite sensor has a predetermined threshold which is set beforehand. When the detected level of deceleration exceeds this threshold, the satellite sensor transmits an output signal indicating a threshold excess to the main controller. In view of the need to reduce the number of cables installed in the vehicle and so on, a serial communication system is used as the communication system between the satellite sensors and the main controller.
In this type of communication control device for passenger protection device, since digital signals are constantly transmitted from the satellite sensors to the main controller, the overall communication control device consumes considerable power, and noise is constantly generated by the transmitted output signals. Accordingly, to reduce power consumption and noise, there is proposed a communication control device for passenger protection device which includes a transmission prohibition unit which, when the detected values and calculated values of the satellite sensors are below a predetermined value with respect to the threshold for determining collision, prohibits transmission of output signals of these detected values and calculated values. According to this communication control device for passenger protection device, when the detection values and calculation values of the satellite sensors are below a predetermined value with respect to the threshold for determining collision, transmission of output signals of these detected values and calculated values is prohibited, thereby enabling power consumption and unwanted noise to be reduced (e.g., see Japanese Patent No. 3206469).
In the communication control device for passenger protection device disclosed in the above Patent Literature, when the output of the detected value or the calculated value from a satellite sensor is zero, the communication control device for passenger protection device cannot determine whether: (a) the output has been determined to be less than a predetermined value with respect to the threshold for determining collision whereby output is prohibited, or (b) there is a malfunction in the satellite sensor itself, making transmission impossible. Therefore, to determine one of these two states, a determination unit and circuits and the like for the determination unit must be separately provided to the communication control device for passenger protection device.